Potentiometer



Oct. 22, 1963 M. NIRENBERG ETAL 3,108,244

POTENTIOMETER Filed July 18, 1961 2 Sheets-Sheet 1 FIG. I. I! l k A JINVENTORS MORRIS Men/sees A! 21 2;

MICHAEL \S'EKE' Q/C 8Y2 a 9L ATTORNEYS 1963 M. NIRENBERG ETALPOTENTIOMETER 2 Shets-Sheet 2 Filed July 18, 1961 FIG. 4.

RIC

ATTORNEYS United States Patent 3,108,244 POTENTIOMETER Morris Nirenberg,Queens, and Michael Sekerich, Brooklyn, N.Y., assignors to VogueInstrument Corporation, Brooklyn, N.Y., a corporation of New York FiledJuly 18, 1961, Ser. No. 124,913 11 Claims. (Cl. 338-144) The presentinvention relates generally to variable electrical resistancestructures, and in particular to an infinite resolution wire woundpotentiometer.

Potentiometers are available on the market which comprise a non-metalliccylindrical wire form which has its outer surface formed with acontinuous helical groove having mounted therein a helically woundresistance wire. The opposite ends of the resistance wire are electrically connected to appropriate terminals and a movable electricalcontact is made to successive portions of the resistance wire by a wiperarranged contiguous to the outer surface of the wire form. The wiperunderlies and engages the resistance wire and is rotatably mounted, asby being connected directly to a control shaft. Accordingly, the wipermay be rotated into various adjusted positions wherein successiveportions of the resistance wire are lifted out of the helical groove andprovide an adjustable and stepless output as a function of the adjustedposition of the wiper.

Potentiometers of this type, which are particularly suited for use inservo mechanisms, should have a number of essential characteristicsincluding, without limitation, the provision of a truly stepless output,a virtually linear output, and a relatively low order of inductance andcapacitance to facilitate use in alternating current circuits.Additionally, and in operation, it is important that the potentiometerproduce low noise, be capable of operation at relatively low torque, andhave a long life despite the wear incident to the continuous adjustmentof the potentiometer and the sliding contact between the wiper and theresistance wire.

Broadly, it is an object of the present invention to provide an improvedwire wound potentiometer of the in finite resolution type which iscapable of realizing one or more of the aforesaid objectives.Specifically, it is within the contemplation of the present invention toprovide an improved mounting and controlling arrangement for the wiperor brush of a potentiometer such that the wiper will exactly follow thehelical path of the resistance wire, thus minimizing sliding or helicalerror between the wiper and the resistance wire and insuring extremelylong wire life, true stepless output, high accuracy and a relatively loworder of electrical noise.

in accordance with an illustrative embodiment demonstrating objects andfeatures of the present invention, there is provided an infiniteresolution potentiometer which comprises a mounting plate, a cylindricalwire form of an insulating material projecting from the mounting plateand having an outer surface formed with a continuous helical groove, anda helically wound resistance wire mounted within the groove. Preferably,the wire form is fabricated of a material of good dimensional stabilityand a low thermal coefficient of linear expansion, resulting inextremely high insulation resistance, low inductance and low capacitancefor use in alternating current applications. A lead screw is secured tothe mounting plate and projects within and along the longitudinal axisof the wire form and carries a follower in threaded engagementtherewith. A wiper is arranged contiguous to the outer surface of thewire form and has a contact section underlying and engaging theresistance wire. The wiper is mounted on the follower for movement alonga helical adjustment path coextensive with the resistance wire. Controlmeans are operatively connected to the follower for rotating thefollower on the lead screw to move the wiper along the adjustment path.The control means includes a control shaft journal-led in the mountingplate and extending coaxially of and through the lead screw and meanscoupling the control shaft to the follower. The potentiometer iscompleted by the provision of terminal means electrically connected tothe opposite ends of the resistance wire and a collector electricallyand rotatably connected to the wiper for providing an appropriatetapotf. The lead screw and follower may be machined to an exceptionallyhigh order of accuracy and with the same pitch as the helically woundresistance wire to assure that the wiper or brush will follow the exacthelical path of the resistance wire, with substantially no sliding orhelical error.

The above brief description, as well as further objects, features andadvantages of the present invention will be more fully appreciated byreference to the following detailed description of presently preferred,but nonetheless illustrative embodiments in accordance with the presentinvention, when taken in conjunction with the accompanying drawings,wherein:

FIG. 1 is an elevational view of an infinite resolution potentiometerdemonstrating features of the present invention, with the cylindricalcase or cover sectioned to reveal the contents thereof;

FIG. 2 is an elevational view taken from the right of FIG. 1, with thecase of cover sectioned and with parts broken awa FIG. 3 is a sectionalview taken substantially along the lines 3-3 of FIG. 1 and looking inthe direction of the arrows;

FIG. 4 is a sectional view taken substantially along the lines 4-4 ofPEG. 3, looking in the direction of the arrows and with a portion of thecase broken away;

PEG. 5 is a sectional view taken substantially along the lines of 5-5 ofFIG. 4 and looking in the direction of the arrows; and

FIG. 6 is a sectional view similar to FIG. 3 but showing a modificationin the collector for electrically connecting the rotatable andlongitudinally movable wiper to an appropriate terminal.

Referring now specifically to the drawings, there is shown in FIGS. 1 to5 inclusive a potentiometer 10' which illustrates features of thepresent invention and includes a housing 12 having a mounting or baseplate 14 and a reinovable cylindrical case or cover 16. The mounting orbase plate 14 is appropriately dimensioned and shaped for mounting in anenvironment structure and is formed in a marginal seat 14a whichreceives the adjacent end of the removable case or cover :16. In atypical construction, both the mounting plate 14 and the cover 16 may befabricated of anodized aluminum or similar light weight material.

Projecting from the mounting plate 14 internally of the case '16 is acylindrical wire forin 1'8 which is fabricated of an appropriatenon-metallic material having good dirnension-al stability and a lowthermal coefficient of linear expansion, such as a fiuoro-carbon. Theouter periphery or surface of the cylindrical wire form 18 is providedwith a continuous helical groove 20, shown here for the purposes ofillustration on a greatly exaggerated scale. The helical groove 20,which is precision ground and is of generally V-shaped section (see FIG.3), receives a helically wound resistance wire 22 which may befabricated of a hard drawn chrome-nickel alloy. The depth of the helicalgroove 20 is sufiicient to accommodate the resistance wire 22 within theconfines of the groove (see FIGS. 3 to 5 inclusive). Although only onegroove cross section has been illustrated, it will be appreciated thatother groove cross sections will be suitable for accommodating theresistance wire.

The cylindrical wire form 155 is mounted within the case 16 by theprovision of an annular retaining flange 1412 on the mounting plate '14(see H68. 3 and 4) which has an outer diameter substantially equal tothe inner diameter of the wire form 18. The wire form 18 is fitted overthe annular retaining flange 14b and is secured to the mounting plate 14coaxially thereof by the provision of one or more mounting bolts 2 (seeFIGS. 4 and 5) which extend lengthwise through the wire form 18- and arethreaded into appropriately tapped holes 140 formed in the adjacent endof the mounting plate 14 at locations spaced radially outwardly of theretaining flange 14b.

The mounting plate 14 supports a stationary hollow lead screw 26 whichprojects within and along the longitudinal axis of the wire form -13.Specifically, and as seen best in FIG. 3, the stationary lead screw 26includes an integral lead screw mounting section 26:: and a threadedsection 26b. The mounting section 26a has an outer diametersubstantially equal to the inner diameter of the annular retainingflange 1412 such that the mounting section 26a may be oriented to havethreaded section 26 project axially of the wire form l8. The mountingsection 26:: is secured to the mounting plate '14 within the annularretaining flange 14b by a number of mounting bolts 28. The threaded orlead screw section 26b is formed with a through bore 260 and projectsbeyond the wire form 18, for a purpose to be subsequently described.

The threaded section 26b of the lead screw 26 carries a followerassembly 36 which includes a follower nut 32 in threaded engagement withthe lead screw section 26b, an insulating block 34 secured to thefollower nut 32, a substantially L-shaped mounting arm 36 ofelectrically conductive material secured to the insulating block 3 3-,and a wiper or brush 38 secured to the mounting arm 36. The wiper orbrush 38 extends generally parallel to the longitudinal axis of the wireform 18 and terminates in a contact section 38a which underlies andengages successive portions of the resistance wire 22.

As will subsequently be described, the follower assembly 30 is rotatedabout and along the lead screw 26 to move the wiper or brush 38 along ahelical adjustment path coextensive with the resistance wire 22 suchthat the transverse segment of the contact section 38a underlying theresistance wire 22 may make continuous contact with successive portionsof the restistance wire 22. The transverse segment of the contactsection 33a underlying the resistance wire 22 may be slightly grooved ornotched to preclude sidewise displacement between the contact and theresistance wire. However, it will be appreciated that the provision ofsuch groove or notch is optional since the pitch of the lead screwsection 26!) and the pitch of the helical groove 2% is the same and maybe held to extremely close tolerances due to the precision grinding orcutting of the lead screw and of the wire groove. In a typical assembly,the wiper or brush 33 is fabricated of a resilient alloy, such asberyllium-copper and is formed with a re duced neck 38b intermediate thecontact section 38a and the mounting arm 36 to allow the contact section38a to flex. The contact section is bowed on an :arc corresponding tothe outer periphery of the wire form 18 such :as not to present anysharp discontinuity to the resistance wire 22 as the contact sectionmoves therebeneath. The contact section 38a may be of precious metal,such as a platinum alloy.

A control assembly or mechanism is operatively connected to the followernut 32 for rotating the follower nut 32 on the lead screw 26 to move thecontact section 38a of the wiper or brush 3% along the adjustment pathin electrical contact with the resistance wire 22. The control assemblyor mechanism includes a control shaft =40 which has a mounting section40a extending through a centrally disposed and axially extending bore Mdin the mounting plate =14 and a reduced diameter control section 41!];which extends through the bore of the lead screw 26 an terminates at alocation spaced beyond the free end thereof. The mounting section iitaof the control shaft 4% is journalled within the mounting plate 14 bythe provision of two precision bearings 42, '44 which have their outerraces secured to the mounting plate 14 and have their inner racessecured to the mounting section itia, with the control shaft 445* beingheld against endwise play by appropriate washers or stops &6, 48.

The control section 40b carries a crosshead 50 which is secured to thecontrol section 4% of the control shaft as in any appropriate fashion,as by the pin 52 (see FIG. 3). The cross head 59 in turn carries a pairof spaced and parallel drive fingers 54, 56 which project from the crosshead 5% towards the follower nut 32 at opposite side of and equallyspaced from the control shaft 49. The drive fingers 54, 56 are slidablyengaged in diametrically opposed cutouts 32a, 321) (see FIG. 5) formedin the follower nut 32. In response to rotation of the control shaft 40,the crosshead 50 and drive fingers 54, 56 will rotate and cause thefollower nut 32 to move along the threaded section 26b of the lead screw26, with the follower nut 32 sliding relative to the drive fingers 54,56.

Collector means are electrically and rotatably connected to the wiper 38for providing a tap-01f and stepless output. In this illustrativeembodiment, the collector means includes a collector cylinder'58 whichis fabricated of an appropriate precious metal and is mounted coaxiallyof and within the wire form 18, as seen best in FIGS. 2 to 5 inclusive.The collector cylinder 58 is of suflicient longitudinal extent to beengaged by movable contacts or brushes 60 which are electricallyconnected to the wiper mounting arm 36 and supported there on inengagement with the inner peripheral surface of the collector cylinder58. The movable contacts 60 are fabricated of any appropriate springymaterial which biases the same into contact with the collector cylinder58, with the cont-act '60 moving along a helical contact path inresponse to rotation of the follower nut 32 on the lead screw 26. Thestepless output is made available .at a tapolf lead 62 which iselectrically connected to the coleetor cylinder 58 and extended througha cutout 18a and the wire form 18.

Terminal connections are provided to the opposite ends of the resistancewire 22 in any appropriate fashion. In this illustrative embodiment, twoterminal strips 64, 66 are mounted longitudinally of land within thewire form 18 (see FIGS. 1 and 3) at locations radially inwardly of theouter periphery of the wire form. The terminal strip 64 has anelectrical connection to the end of the resistance wire 22 contiguous tothe mounting plate 14, and to a terminal lead 68, while the terminalstrip 66 has an electrical connection to the end of the resistance wire22 remote from the mounting plate 14 and an electrical connection to aterminal lead 70.

Mechanical end stops are provided to limit the traverse of the followernut 32 on the lead screw 26 and the corresponding traverse of the wiperor brush 38 along the resistance wire 22. In this illustrativeembodiment, the follower nut 32 is provided with movable stop pins 72,74 projecting from the opposite face thereof. The stop pin 72 limits thetravel of the follower nut to the right in FIGS. 3 and 4 while the stoppin 74 limits the travel of the follower nut to the left in FIGS. 3 and4. Specifically, the stop pin 72 cooperates with an adjustable end stop76 which is secured to the stationary lead screw section 26b adjacentthe free end thereof inwardly of the cross head 50. The end stop 76carries. a stationary stop pin 78 which is radially spaced from thelongitudinal axis of the lead screw 26 to be contacted by the movablestop pin 72. The end stop 76 is bifurcated and pro vided with opposedears 76a, 76b (see FIG. 2) which ears are traversed by an adjustment andlocking screw 8% which enables the release and securement of the endstop 76 in any adjusted position on the lead screw section 26b. Traverseof the follower nut 32 in the opposite direction and towards themounting plate 14 is limited by contact of the movable stop pin 74 witha stationary stop pin 82 fixed to and projecting inwardly from the leadscrew mounting section 26a at a location readily spaced from thelongitudinal, axis of the lead screw 26 and along the path of themovable stop pin 74 (see FIG. 4).

A typical sequence of operations will now be described in order tofacilitate a more thorough understand ing of the invention.

When the potentiometer is incorporated into an operating environment ofsystem and input is applied to the control shaft 40, eitherautomatically or manually, rotation of the control section 40b willcause a corresponding rotation of the crosshead 50 and of the drivefingers 54, 56. The drive fingers 54, 56 due to their coupling with thefollower nut 32, will cause the same to rotate about and traverse alongthe lead screw section 26b thereby imparting a corresponding motion tothe follower assembly 30 and the Wiper 38. The segment of the contactsection 38a underlying the resistance wire 22 will move in a helicalpath corresponding to the pitch of the lead screw 26 and to thecomparable pitch of the groove 20 thereby providing a stepless outputwhich will be a function of the relative position of the contact section38a along the resistance wire 22. The contact pressure of the wiper orbrush 38 may be established to provide relatively low frictional contactwith the resistance wire 22 yet achieving the necessary electricaltapoff thereby assuring long life and relatively low wear. Further,since the wiper or brush 38 follows the exact helical path of theresistance wire 22 there Will be a minimum sliding or helical errorbetween the contact and wire. By appro priate selection of materials andcontrol in manufacturing tolerances, a high order of linearity may beattained for the potentiometer and optimum mechanical conditions may beestablished for the product.

Reference will now be made to FIG. 6 which shows a modification of thehigh resolution potentiometer, particularly in the construction of thecollector means which electrically and rotatably connects the movablewiper or brush to the resistance wire for providing the stepless output.Since the construction of this potentiometer is subsubstantiallyidentical to that previously described, corresponding parts will bedesignated by the same reference numeral as a part of a 100 series andthe detailed de scription will be limited only to the construction ofthe collector means which may be employed in lieu of the collectorcylinder 58 and the brushes 6t Specifically, an annular collector ring158 is mounted on the end face of the wire form 118 remote from themounting plate 114-. The collector ring, which is in the form of a fiatannulus, is disposed concentrically of the lead screw 126 andelectrically contacted by the movable contacts or brushes 160 which aremounted on the cross head 156 by an appropriate insulating block 161.The insulating block 161 is secured to the cross head 150 by appropriatemounting screws or bolts 163, while the brushes 16d are connected to aterminal plate 165 which is riveted or otherwise secured to theinsulating block 161. The electrical connection from the brushes 16% viathe terminal plate 165 to the wiper mounting arm 136 and to the brush orwiper (not shown but comparable to the brush or wiper 138) is completedby the provision of a jumper wire 167 which is electrically connected atone end to the terminal plate 165 and at the other end to the wipermounting arm 136. The jumper wire 167 is flexible and is of suificientlength such as not to interfere with the movement of the follower nut132 along the lead screw 126 and yet provides the necessary electricalconnection between the movable follower assembly and the stationarycollector ring 158. In this embodiment, it will be appreciated that thebrushes 160 traverse the same annular contact paths on the collectorring 158 and may be initially constructed to be of a relatively narrowwidth comparable to the spacing between the brushes. Obviously, thisrepresents a saving as compared to the use of the relatively longcylindrical collector ring 58 and results in manufacturing economies,particularly when it is recalled that the collector ring is usuallyfabricated or plated of a precious metal.

A latitude of modification, change and substitution is intended in theforegoing disclosure and in some instances some features of theinvention will be employed without a corresponding use of otherfeatures. Accordingly it is appropriate that the appended claims beconstrued broadly and in a manner consistent with the spirit and scopeof the invention herein.

What we claim is:

1. An infinite resolution potentiometer comprising a mounting plate, acylindrical wire form of an insulating material projecting from saidmounting plate and having an outer surface formed with a continuoushelical groove, a helically wound resistance wire mounted within saidgroove, a stationary lead screw secured to said mounting plate andprojecting within and along the longitudinal axis of said wire form, afollower in threaded engagement with said lead screw, a wiper arrangedcontiguous to said outer surface of said wire form and having a cont-actsection underlying and engaging said resistance wire, means mountingsaid wiper on follower for movement along a helical adjustment pathcoextensive with said resistance wire, and control means operativelyconnected to said follower for rotating said follower on said lead screwto move said wiper along said adjustment path.

2. An infinite resolution potentiometer comprising a mounting plate, acylindrical wire form of an insulating material projecting from saidmounting plate and having an outer surface formed with a continuoushelical groove, a helically wound resistance wire mounted within saidgroove, a stationary hollow lead screw secured to said mounting plateand projecting within and along the longitudinal axis of said wire form,a follower in threaded engagement with said lead screw, a wiper arrangedcontiguous to said outer surface of said wire form and having a contactsection underlying and engaging said resistance wire, means mountingsaid wiper on follower for movement along a helical adjustment pathcoextensive with said resistance wire, and control means operativelyconnected to said follower for rotating said follower on said lead screwto move said wiper along said adjustment path, said control meansincluding a control shaft journalled in said mounting plate andextending coaxially of and through said lead screw and means couplingsaid control shaft to said follower.

3. An infinite resolution potentiometer comprising a mounting plate, acylindrical wire form of an insulating material projecting from saidmounting plate and hav ing an outer surface formed with a continuoushelical groove, a helically wound resistance wire mounted within saidgroove, a stationary hollow lead screw secured to said mounting plateand projecting within and along the longitudinal axis of said wire form,a follower in threaded en gagement with said lead screw, a wiperarranged contiguous to said outer surface of said wire form and having acontact section underlying and engaging said resistance wire, meansmounting said wiper on follower for movement along a helical adjustmentpath coextensive with said resistance wire, control means operativelyconnected to said follower for rotating said follower on said lead screwto move said wiper along said adjustment path, and collector meanselectrically and rotatably connected to said wiper for providing atapofi connection thereto.

4. An infinite resolution potentiometer according to claim 3 whereinsaid collector means includes a collector cylinder coaxial-1y of andwithin said wire form, and brush means in rotatable contact with saidcollector cylinder and electrically connected to said wiper.

5. An infinite resolution potentiometer according to claim 3 whereinsaid collector means includes an annular collector ring extendingtransversely of said longitudinal axis and mounted on said wire form,and brush means in rotatable contact with said Collector ringand'electrically connected to said wiper.

6. An infinite resolution potentiometer comprising a mounting plate, acylindrical wire form of an insulating material projecting from saidmounting plate and having an outer surface formed with a continuoushelical groove, 3. helically wound resistance wire mounted within saidgroove, a stationary hollow lead screw secured to said mounting plateand projecting within and along the longitudinal axis of said wire form,a follower in threaded engagement with said lead screw, a wiper arrangedcontiguous to said outer surface of said wire form and having a contactsection underlying and engaging said resistance Wire, means mountingsaid wiper on follower tfOl' movement along .a helical adjustment pathcoextensive with said resistance wires, control means operativelyconnected to said follower for rotating said follower on said lead screwto move said wiper along said adjustment path, said control meansincluding a control shaft journalled in said rounting plate' andextending coaxially of and through said lead screw and means couplingsaid control shaft to said follower, collector means electrically androtatably connected to said wiper for providing a tapofi connectionthereto, and terminal means electrically connected to the opposite endsof said resistance wire.

7. An infinite resolution potentiometer according to claim 6 whereinsaid collector means includes a collector cylinder coaxiaily of andwithin said wire form, and brush means in rotatable contact with saidcollector cylinder and electrically connected to said wiper.

8. An infinite resolution potentiometer according to claim 6 whereinsaid collector means includes an annular collector ring extendingtransversely of said longitudinal axis and mounted on said wire form,and brush means in rotatable contact with said collector ring andelectrically connected to said wiper.

9. In an infinite resolution potentiometer, mounting means including awire form having a helical groove, a resistance wire mounted in saidgroove, a stationary lead screw supported on said mounting means andextending axially of said resistance Wire, said lead screw having apitch substantially corresponding to the pitch of said helical groove, afollower engaging said lead screw and 8 control meansopcratively'connected to said follower for rotating said follower.

10. An infinite resolution potentiometer comprising mounting meansincluding a wire form having a helical groove, a resistance wire mountedin said groove, a stationary lead screw supported on said mounting meansand extending axially of said resistance wire, said lead screw having apitch substantially corresponding to the pitch of said helical groove, afollower engaging said lead screw and movable therealong in response tobeing rotated, a brush underlying said resistance wire and operativelyconnected to said follower for movement therewith and making contactwith successive portions of said resistance wire, control means operatively connected to said follower for rotating said follower, collectormeans electrically connected to said brush and including a stationaryterminal providing a stepless output from said brush, and terminal meanselectrically connected to the opposite ends of said resistance wirerespectively.

ll. An infinite resolution potentiometer comprising mounting meansincluding a wire form having a helical groove, a resistance wire mountedin said groove, a stationary lead screw supported on said mounting meansand extending axially of said resistance wire, said lead screw having apitch substantially corresponding to the pitch of said helical groove, afollower engaging said lead screw and movable therealong in response tobeing rotated, a brush underlying said resistance wire and operativelyconnected to said follower for movement therewith and making contactwith successive portions of said resistance wire, control meansoperatively connected to said follower, said control means including acontrol shaft journal-led on said mounting means and extending coaxiallyof and through said lead screw and drive means carried on said controlshaft and slidably coupled to said follower for rotating said follower,collector means electrically connected to said :brush and including astationary terminal providing a stepless output from said brush, andterminal means electrically connected to the opposite ends of saidresistance wire respectively.

movable therealong in response to being rotated, -a brush underlyingsaid resistance wire and operatively connected to said tfollower :formovement therewith and making contact with successive portions of saidresistance wire, and

References Cited in the file of this patent UNITED STATES PATENTS2,773,966 Mastropole Dec. 11, 1956 2,813,182 Van Alen Nov. 12, 19572.887.555 Marason May 19, 1959

1. AN INFINITE RESOLUTION POTENTIOMETER COMPRISING A MOUNTING PLATE, ACYLINDRICAL WIRE FORM OF AN INSULATING MATERIAL PROJECTING FROM SAIDMOUNTING PLATE AND HAVING AN OUTER SURFACE FORMED WITH A CONTINUOUSHELICAL GROOVE, A HELICALLY WOUND RESISTANCE WIRE MOUNTED WITHIN SAIDGROOVE, A STATIONARY LEAD SCREW SECURED TO SAID MOUNTING PLATE ANDPREJECTING WITHIN AND ALONG THE LONGITUDINAL AXIS OF SAID WIRE FORM, AFOLLOWER IN THREADED ENGAGEMENT WITH SAID LEAD SCREW, A WIPER ARRANGEDCONTIGUOUS TO SAID